river
Capitalize river when it precedes or follows a proper name:
Mississippi River, the River Mississippi
For plurals write:
Mississippi and Missouri Rivers
the Rivers Mississippi and Missouri
Rhine River system
but Rhine and Danube river systems
Capitalize river when it precedes or follows a proper name:
Mississippi River, the River Mississippi
For plurals write:
Mississippi and Missouri Rivers
the Rivers Mississippi and Missouri
Rhine River system
but Rhine and Danube river systems